The present invention relates to pipeline connection apparatus, particularly, but not exclusively, pipeline connection apparatus for connecting a pipeline coupling of a first subsea structure, such as a pipeline branch, manifold or termination, to a pipeline coupling of another such structure by way of a spool or jumper arrangement
In modern subsea oil and gas exploration and production systems it is common to install a number of subsea structures on the seabed and to connect them together when flow of production between the structures is required. The procedure for connecting a pipeline coupling on one subsea structure to that of another can be complicated since it can be very difficult to position the subsea structures accurately enough on the seabed such that the pipeline coupling of one structure is suitably aligned with that of the other. Another problem encountered is that the pipeline between the structures tends to flex under the effect of temperature and pressure changes which can result in undesirable movement of the structures themselves and the pipeline system as well as increased stress loads.
In an attempt to minimise these problems, it is common to provide a spool or jumper arrangement between the couplings on the structures. The terms ‘spool’ and ‘jumper’ are used in this context to refer to a section of pipeline dimensioned to make the connection between a first subsea structure and a second subsea structure. Various terms are in use, and the term ‘spoolpiece’ will be used herein, without intending any limitation as to the particular form of jumper or spool concerned. The pipe of the spool or jumper in this context is essentially rigid but, by the incorporation of bends, for example, the spoolpiece, provides an important degree of flexibility to absorb relative motion, due to thermal or pressure induced expansion, between the two structures.
Examples of subsea structures connected by a spoolpiece could be a pipeline and riser, a pipeline and fixed subsea structure, or a pair of fixed structures such as a wellhead and manifold. It will be known that a seabed pipeline is generally terminated by some sort of structure to stabilise the pipe and provide some support to the connection with the spoolpiece, and also to provide adequate interface between pipeline/spool and seabed. Such a structure generally is built upon a base structure incorporating a ‘mudmat’, with the aim to anchor the pipe either totally or partially but generally limit the freedom of the pipe to move in relation to the seabed. This eliminates the uncertainties associated with the soil and its interface with the pipeline.
The spoolpiece thus provides a connection for flow of fluid between the subsea structures which compensates for any misalignment between the respective couplings on the subsea structures. The degree of adjustment, if any, provided by the spoolpiece alone is limited. In situations where the misalignment between the subsea structures is relatively large, it is common that a relatively large and cumbersome spoolpiece must be installed in order to achieve the required connection between the misaligned subsea structures, and/or to provide the required degree of flexibility. Such arrangements also require the spoolpiece to be fabricated with very tight tolerance levels, which can increase costs and complexity.
According to a first aspect of the present invention there is provided a method of making a connection to a subsea pipeline, the method comprising:—
(a) connecting said pipeline to a first end of a pipeline connecting piece having first and second ends;
(b) supporting the pipeline connecting piece on a subsea base structure;
(c) before or after step (b) preparing a second pipeline adapted for connection to the second end of the connecting piece and positioning the second pipeline for connection to the second end of the connecting piece;
(d) applying one or more adjustable constraints to align the second end of the connecting piece with the end of the second pipeline and completing connection of the connecting piece to the second piece of pipeline; and
(e) after completing the connection removing said constraint(s) so that the connecting piece is free to move in at least two dimensions over the subsea base structure.
In the finished installation the connecting piece may be free to move in relation to the base structure with four or five degrees of freedom (for example directions Y, X, ROTX, ROTY, ROTZ) while being supported at a well-defined elevation in a vertical (Z) direction.
The adjusting in step (d) may be performed using one or more actuators acting between the connecting piece and the base structure, the base structure remaining substantially unmoved.
The adjusting in step (d) can include adjusting a roll angle of the connecting piece, including rotation of the attached end of the first pipeline. The rotating action may be provided by a variable length actuator extending between the base structure and a cross bar supporting one side of the connecting piece. Preferably a pair of actuators are provided to effect roll in opposite directions.
The roll actuator(s) may be operable by remote operated vehicle (ROV). This allows a simple screw jack or the like to be provided at low cost, with motive power and control systems being provided on the ROV.
The roll actuator(s) may be removed or retracted in step (e) so as to leave the connecting piece free to roll in response to operating forces in the connected pipelines.
The adjusting in step (d) may include adjusting the pitch angle of the connecting piece by selectively lifting or lowering the first piece of pipeline relative to the seabed.
The adjusting step may include laterally moving the first end of the pipeline connecting piece using suitable transverse actuation means. The transverse actuation means may comprise a pair of hydraulic cylinders provided on either side of the pipeline connecting piece. The transverse actuation means may be removed or otherwise disengaged in step (e), leaving the connecting piece free to translate in response to operating forces in the connecting pipelines.
The connecting piece may be connected on the base structure by an articulated support permitting at least two rotational degrees of freedom (such as roll, pitch and/or yaw).
The base structure preferably includes a skid surface, the connecting piece being supported on a skid foot so as to permit translation in two dimensions parallel to the skid surface and rotation about an axis normal to the skid surface.
The skid foot may be shaped so as to provide at least one of said four or five degrees of freedom by rolling.
The articulated support may include at least one hinge between the connecting piece and the skid foot so as to provide at least one of said four or five degrees of freedom by rotation of the hinge.
Many different structures for the articulated support may be envisaged, depending which degrees of freedom are to be provided by the shape of the skid foot, and which are provided by articulation between the skid foot and the connecting piece. For example, a flat skid foot could be coupled to the connecting piece via a ball joint or universal joint which provides two or three rotational degrees in addition to two translational degrees provided by skidding. At the other extreme a rigid connection may be provided between the connecting piece and the skid foot, the foot having a ball shape so as to permit two rotational degrees of freedom by rolling on the skid surface, and two translational and one rotational degree of freedom by skidding.
In a preferred embodiment described further below, there is provided a skid foot having a part-cylindrical skid surface to provide a first rotational degree of freedom by rolling while providing two translational degrees and a second rotational degree of freedom by skidding. The skid foot in that embodiment is connected to the connecting piece by a pivot joint so as to provide a third rotational degree of freedom.
The second piece of pipeline may be a spool piece connecting the first pipeline via said connecting piece to a fixed seabed structure.
The step (e) may include removing a lateral constraint on the connecting piece such that it may skid freely in two dimensions and yaw over the base structure after installation. This allows the entire pipeline structure to accommodate various operational forces by moving, rather than by resistance in strength and weight or increased spool spans.
The invention in the first aspect further provides a pipeline termination component comprising a pipeline connecting piece joined to at least part of the articulated support for use in the method of the invention as set forth above.
The invention in the first aspect yet further provides a subsea pipeline installation wherein a connecting piece has been deployed by a method as set forth above.
The invention in a second aspect provides a pipeline termination device comprising:—                a pipeline connecting piece for connecting a first piece of pipeline to a second piece of pipeline;        an articulated support provided on the pipeline connecting piece for supporting it on a seabed skid base, wherein the articulated support in use allows the pipeline connecting piece orientation to be adjusted relative to the skid base in with least two rotational degrees of freedom in addition to translation by skidding.        
The articulated support may include a skid foot so as to permit translation in two dimensions parallel to the skid surface and rotation about an axis normal to the skid surface.
The skid foot may be shaped so as to provide at least one of said rotational degrees of freedom by rolling.
The articulated support may include at least one pivot between the connecting piece and the skid foot so as to provide at least one of said rotational degrees of freedom by rotation about the pivot.
Many different structures for the articulated support may be envisaged, as discussed already above.
In a preferred embodiment, there is provided a skid foot having a part-cylindrical skid surface to provide a first rotational degree of freedom by rolling while providing two translational degrees and a second rotational degree of freedom by skidding. The skid foot in that embodiment is connected to the connecting piece by a pivot joint so as to provide a third rotational degree of freedom.
The connecting piece may be provided with roll arms extending transversely, the apparatus including means for raising at least one of said roll arms selectively in order to alter the roll angle of the pipeline connecting piece relative to the base structure.
One end of the pipeline connecting piece may be connected to a pipeline of a subsea pipeline system and the other end may be connected to a spoolpiece connected to another subsea structure.
The connecting piece may be provided in combination with a skid base adapted for providing a skid surface at a desired location on the seabed.
The skid base may further be provided with a guide gate for guiding the pipeline connecting piece onto the base structure. The or each guide gate may be removable from the base structure, so as to permit transverse movement of the connecting piece after installation.
The combination may be provided with actuation means capable of laterally moving the pipeline connecting piece in order to adjust lateral offset of the pipeline connecting piece relative to the skid base structure. The actuation means may comprise at least one hydraulic cylinder mounted on uprights of the guide gate, where provided.
The apparatus may further comprise means for adjusting a pitch angle of the connecting piece. The pitch adjusting means may be adapted to lift a portion of the subsea pipeline at a suitable distance from the apparatus, the connecting piece pitching about an axis defined by the articulated support.
The invention in the second aspect yet further provides a subsea pipeline installation including a pipeline termination device according to the invention as set forth above.
The invention in a third aspect provides a seabed pipeline installation wherein a pipeline end termination or inline module connected to a first pipeline is supported on a seabed skid base with four or five degrees of freedom of movement relative to the skid base.